Materials for Engineering Unit II

Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 1
Materials for Engineering [20ME11T]
Unit II- Notes
Contents
STEELS AND ALLOYS
2.0 Cast Iron
2.1 Types of cast iron
2.1.1 White
2.1.2 Grey
2.1.3 Nodular
2.1.4 Malleable
2.2 Selection of appropriate cast iron for engineering application
2.3 Steel
2.4 Broad classification of steels
2.4.1 Plain carbon steels
2.4.2 Alloy steels
2.4.3 Tool steel
2.4.4 Stainless steel
2.5 Spring steel-composition and application
2.6 Steels for following-shaft -axles-bolts-nuts-Agriculture Equipment’s-household utensils-
Antifriction bearings.
2.7 Designation and coding (as per BIS, ASME) of plain & alloy steel and cast iron.

2.0 Cast Iron
Cast iron is an alloy of iron and carbon in which the carbon is present in the range of 2-4 % by
wt and silicon is present in between 1-3 % by wt. Some Other alloying elements that added to
cast iron are manganese, molybdenum, chromium, magnesium, titanium, vanadium, nickel,
copper, tin, zirconium, bismuth, boron. The melting point of cast iron ranges in between 1127 to
1204 degree Celsius. The alloying elements are added in order to control the percentage of the
carbon and silicon as well as to give desired properties to the cast iron. The percentage of the
carbon and silicon decides which type of cast iron is produced.
Properties of Cast Iron
a) Brittle: Cast iron is brittle except malleable cast iron. (Brittle means, it breaks into small
pieces when hammered).
b) Low Melting Point: It has a low melting point (1127ºC– 1204ºC)
c) Fluidity: It possesses good fluidity ( The ability to flow easily in a molten state)
d) Cast ability: It possesses good cast ability. Cast ability is defined as the ability to be cast into
new parts in the casting process.
e) Machinability: It has good machinability. Machinability is defined as the ability of a metal
that allows being cut (machined) easily with a good surface finish at a low cost.
f) Resistance to deformation and wear resistance: It has excellent resistance to deformation
i.e. it does not changes its shape when force is applied to it. It also has wear resistance which
means that it opposes the damage in normal usage
How Cast Iron is Produced

Cast iron (CI) is produced from the pig iron. And pig iron is produced by melting iron ore in a
blast furnace. The pig iron is converted into ingots and then these ingots are re-melted again to
produce cast iron. CI can also be produced directly from the molten pig iron.
2.1 Types of cast iron
By controlling the percentage of carbon and silicon in the molten pig iron and adding alloying
elements we can get different types of cast iron. And these are
2.1.1 White Cast Iron
It is a type of cast iron that contains 3.4 % carbon, 1.5 percent silicon, and .5 % manganese. It is
called as white cast iron because it shows white cracks when fractured. It is the only member of
the cast iron family which is free from graphite. It mainly consists of Iron Carbide in its
microstructure that makes it hard and brittle. It is produced by the rapid cooling of the molten pig
iron.
Properties
a) It is hard and brittle.
b) Cannot be machined easily.
c) It is light in appearance because of the absence of graphite.
d) It has high compressive strength and it also retains its hardness and strength even at high
temperatures.
e) Good abrasion resistance.
Application
a) It is used to make wear surfaces such as impeller and volute of slurry pumps,
b) In ball mills, it used to make shell liner and lifter bars.
c) In coal pulverizers, it used to make balls and rings.
d) In excavating machine, the teeth of the digging bucket are made with white cast iron.

2.1.2 Grey Cast Iron
When molten pig iron in the presence of alloying elements is cooled moderately or slowly, we
get grey cast iron. It has graphitic (i.e. graphite flakes is present in it) microstructure and shows
grey color cracks when fractured.
Due to the formation of grey cracks, it is named as grey cast iron. It is the most widely
used cast iron based on weight among all types. If molten pig iron is cooled on a moderate rate
then we get pearlitic gray cast iron and cooling on slow rate gives us ferritic gray cast iron.
Properties
a) Low tensile strength
b) It has good stiffness.
c) It has high thermal conductivity and specific heat capacity.
d) Easy to machine, due to the presence of graphite flakes.
e) Good damping capacity that allows it to used as the base for the machine tool mountings
Application
a) Because of its stiffness, it is used to make housing of cylinder blocks of internal
combustion engine, housings of pumps, Valve bodies, decorative castings, and electrical
boxes.
b) It has high thermal conductivity and specific heat capacity that make it perfect to make disc
brake rotors and cast iron cookware.
c) It is used as a base for machine tool mountings because of its very good damping capacity.

2.1.3 Nodular or Ductile Cast Iron
Ductile cast iron has nodular (spheroidal) graphite in its microstructure. It is also known as
nodular cast iron, spheroidal graphite cast iron. Keith Millis in 1943 discovered ductile cast iron.
Ductile cast iron is produced by adding nodulizing agent Magnesium in the molten pig iron that
helps to convert graphite into nodules. Cerium, Tellurium, and Yttrium are also possible
nodulizer that can be used.
Properties
Most of the ductile cast has similar properties with the malleable cast iron.
It has good impact and fatigue resistance due to the presence of nodular graphite.
Application
It is used to produce ductile iron pipe that is used for water and sewer lines.
a) Automotive industry: It used to make many automotive components like connecting rods,
crankshafts, cylinders, disc brake caliper, gears and gearboxes etc.
b) Wind power industry: In the wind power industry, it is used for making hubs and structural
parts like frames of machines.
2.1.4 Malleable Cast Iron
Malleable cast iron is produced from the white cast iron. The white cast iron is heat-treated
(Annealing) at about 950 Degree Celsius for 24 or 48 hrs and then allow to cool for 24 hrs or 48
hrs. This changes the carbon in the iron carbide of the cast iron into graphite and ferrite plus
carbon. Nodular graphite is present in the malleable cast iron.

Properties
a) It has excellent strength and toughness.
b) Very ductile and malleable in nature.
Application
Due to its excellent ductility and tensile strength, malleable CI is used for making electrical
fittings and equipments, pipe fittings, hand tools, washers, farm equipment, brackets, mining
hardware, and parts of machines.
2.2 Selection of appropriate cast iron for engineering application
To understand the application of Cast Iron in engineering field we have to understand the special
features of Cast Iron, they are:
Strength: Cast iron has higher strength at reduced costs. They also have higher strength and
ductility and are stiffer than pure iron. The strength of cast iron is what makes it a workable
material for various industries. It has a low melting point and greater fluidity.
Castability: Cast iron is used in an array of industries because of the ease of its castability. The
cast iron can be molded into various shapes and sizes based on the industrial needs. The cost of
production and the minimal usage of tools make it a viable manufacturing material.
Machinability: Cast iron can be easily machined into final products. The properties of a metal
like hardness, tensile strength and microstructure alter its machinability. Hence, it can be used in
a number of industries for manufacturing numerous products.
Low cost and durability: Cast iron saves tons of money in the long term. It requires little or no
maintenance for a long time coming. Using cast iron in industries can eliminate unnecessary
replacement. Further, cast iron products can be integrated into existing systems, thereby
minimizing the cost of replacement. Cast iron is also more malleable than other metals.
Applications of cast iron
It is used in making following things
a) It is used in making pipes, to carry suitable fluids
b) It is used in making different machines and automotive parts
c) It is used in making pots pans and utensils
d) It is used in making anchor for ships.
e) It has excellent anti-vibration (or damping) properties hence it is used to make machine
frames

2.3 Steel
There are various modified forms of iron, artificially produced, having a carbon content less than
that of pig iron and more than that of wrought iron, and having qualities of hardness, elasticity,
and strength varying according to composition and heat treatment: generally categorized as
having a high, medium, or low-carbon content and named after Steel.
2.4 Broad classification of steels
Classifications of Steel can also be classified by a variety of different factors:
1. Composition: Carbon range, Alloy, Stainless.
2. The production method: Continuous cast, Electric furnace, Etc.
3. Finishing method used: Cold Rolled, Hot Rolled, Cold Drawn (Cold Finished), Etc.
4. Form or shape: Bar, Rod, Tube, Pipe, Plate, Sheet, Structural, Etc.
5. De-oxidation process (oxygen removed from steelmaking process): Killed & Semi-Killed
Steel, Etc.
6. Microstructure: Ferritic, Pearlitic, Martensitic, Etc.
7. Physical Strength (Per ASTM Standards).
8. Heat Treatment: Annealed, Quenched & Tempered, Etc.
9. Quality Nomenclature: Commercial Quality, Drawing Quality, Pressure Vessel Quality, Etc.
According to the American Iron & Steel Institute (AISI), Steel can be categorized into four basic
groups based on the chemical compositions:
1. Plain Carbon Steel
2. Alloy Steel
3. Tool Steel
4. Stainless Steel
There are many different grades of steel that encompass varied properties. These properties can
be physical, chemical and environmental. All steel is composed of iron and carbon. It is the
amount of carbon, and the additional alloys that determine the properties of each grade.

2.4.1 Plain carbon steels
i) Definition
Carbon steel is an iron-carbon alloy, which contains up to 2.1 wt. % carbon. Carbon steel can be
classified into three categories according to its carbon content:
ii) Types
a) Low-carbon steel (or mild-carbon steel),
b) Medium-carbon steel and
c) High-carbon steel.
iii) Properties: Their carbon content, microstructure and properties compare as follows:
Steel Type Carbon content
(wt.%)
Microstructure Properties
Low-carbon steel < 0.25 Ferrite, pearlite
Low hardness and cost. High
ductility, toughness,
machinability and
weldability
Medium-carbon steel 0.25 – 0.60 Martensite
Low hardenability, medium
strength, ductility and
toughness
High-carbon steel 0.60 – 1.25 Pearlite
High hardness, strength, low
ductility
iv) Composition
a) Low Carbon Steel (Mild Steel): It is the most widely used form of carbon steel. These
steels usually have a carbon content of less than 0.25 wt. %. They cannot be hardened by heat
treatment so this is usually achieved by cold work.
Carbon steels are usually relatively soft and have low strength. They do, however, have high
ductility, making them excellent for machining, welding and low cost.

b) Medium Carbon Steel: It has a carbon content of 0.25 – 0.60 wt.% and a manganese
content of 0.60 – 1.65 wt.%. The mechanical properties of this steel are improved via heat
treatment involving autenitising followed by quenching and tempering, giving them a
martensitic microstructure.
c) High Carbon Steel: It has a carbon content of 0.60– 1.25 wt. % and a manganese content of
0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the
lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are
almost always hardened and tempered.
v) Applications
a) Low-carbon steel
Low carbon steels are often used in automobile body components, structural shapes (I-beams,
channel and angle iron), pipes, construction and bridge components, and food cans.
b) Medium-carbon steel
As a result of their high strength, resistance to wear and toughness, medium-carbon steels are
often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring
this combination of properties.
c) High-carbon steel
Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools,
springs high strength wire and dies.
2.4.2 Alloy steels
i) Definition
When other elements comprising metals and non-metals are added to carbon steel, alloy steel is
formed. These alloy steels display various environmental, chemical and physical properties that
can vary with the elements used to alloy. Here the proportion of alloying elements can provide
different mechanical properties.

ii) Effect of alloying
Alloying elements can alter carbon steel in several ways. Alloying can affect micro-structures,
heat-treatment conditions and mechanical properties. Today’s technology with high-speed
computers can foresee the properties and micro-structures of steel when it is cold-formed, heat
treated, hot-rolled or alloyed.
iii) Types of alloy steel
There are two kinds of alloy steel – low-alloy steel and high-alloy steel. As mentioned earlier,
the composition and proportion of alloying elements determine the various properties of alloy
steel. Low-alloy steels are the ones which have up to 8% alloying elements whereas high-alloy
steels have more than 8% alloying elements.
iv) Alloying elements and effect of alloying elements on properties of alloy steel
There are around 20 alloying elements that can be added to carbon steel to produce various
grades of alloy steel. These provide different types of properties. Some of the elements used and
their effects include:
a) Aluminum (Al) – deoxidizer, limits austenite grains growth
b) Chromium (Cr) – improves hardenability, strength and wear resistance, sharply increases
corrosion resistance at high concentrations (> 12%). Copper – can increase corrosion
resistance and harness
c) Manganese (Mn) – improves hardenability, ductility and wear resistance. Mn eliminates
formation of harmful iron sulfides, increasing strength at high temperatures.
d) Nickel (Ni) – increases strength, impact strength and toughness, impart corrosion resistance
in combination with other elements.
e) Silicon (Si) – improves strength, elasticity, acid resistance and promotes large grain sizes,
which cause increasing magnetic permeability.
f) Tungsten (W) – increases hardness particularly at elevated temperatures due to stable
carbides, refines grain size.
g) Vanadium (V) – increases strength, hardness, creep resistance and impact resistance due to
formation of hard vanadium carbides, limits grain size.

2.4.3 Tool steel
Tool steel is the steel be used to manufacture cutting tools, measuring tools, moulds and
antifriction Tool it refers to a variety of carbon and alloy steels that are particularly well-suited to
be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion
and deformation and their ability to hold a cutting edge at elevated temperatures. As a result tool
steels are suited for their use in the shaping of other materials. Tool steels are a family carbon
and alloy steels having distinct characteristics such as hardness, wear resistance, toughness, and
resistance to softening at elevated temperatures. They are classified according to their
composition and properties into various categories.
i) Cold work tool steels are used for gages, blanking, drawing and piercing dies, shears, forming
and banding rolls, lathe centers, mandrels, broaches, reamers, taps, threading dies, plastic molds,
knurling tools. Applications also include moulds for wire cutting, rolling cutters and shaping
wheels in steel tube industry, and wheels, screw moulds, drawing dies in screw industry.
ii) Hot work steels enable the hot-forming of work-pieces made of iron and non-ferrous metals
as well as alloy derivatives at high temperatures. They are utilized in processes such as pressure
die casting, extrusion and drop forging as well as in tube and glass manufacturing. Tools made
from hot-work tool steels are not only subject to constantly high temperatures when employed,
but also to fluctuating thermal loads occurring where the tool surfaces come into contact with the
materials to be processed.

iii) High-speed steels, abbreviated as HSS, are a specialized class of tool steels that were named
primarily for their ability to machine and cut materials at high speeds (high hot hardness). It is
often used in power-saw blades, drill bits, planing and slotting tools, twist drills, Turning,
threading dies, profile cutting tools, broaching tools, reamers.. High-speed steel is superior to the
older high-carbon steel tools in that it can withstand higher temperatures without losing its
temper (hardness). High-speed steels are complex iron-base alloys of carbon, chromium,
vanadium, molybdenum, or tungsten, or combinations of these. To achieve good cutting
performance from HSS, an appropriate hardening response must be provided in heat treatment.
2.4.4 Stainless steel
Steel is an alloy of iron and carbon. Stainless steels are steels containing at least 10.5%
chromium, less than 1.2% carbon and other alloying elements. Stainless steels corrosion
resistance and mechanical properties can be further enhanced by adding other elements, such as
nickel, molybdenum, titanium, niobium, manganese, etc.
i) Properties of Stainless Steels
The advantageous properties of stainless steel can be seen when compared to standard plain
carbon mild steel. Although stainless steel have a broad range of properties, in general, when
compared with mild steel, stainless steel have:
 Higher corrosion resistance
 Higher cryogenic toughness
 Higher work hardening rate
 Higher hot strength
 Higher ductility
 Higher strength and hardness
 A more attractive appearance
 Lower maintenance

ii) Types of Stainless Steel
There are many grades and surface finishes of stainless steel available depending on the environment
the metal is expected to withstand. Based on the microstructure, they can be classified into four major
categories.
a) Austenitic stainless steel
Austenitic stainless steel contains a minimum of 16% chromium and 6% nickel. They range from
basic grades like 304 through to super austenitics such as 904L and 6% Molybdenum grades.
Applications for austenitic stainless steel include:
 Kitchen sinks
 Architectural applications such as roofing and cladding
 Roofing and gutters
 Doors and Windows
 Benches and food preparation areas
 Food processing equipment
 Heat exchangers
 Ovens
 Chemical tanks
b) Ferritic stainless steel
Ferritic steels will usually only have chromium as an alloying element. The chromium content ranges
from 10.5 to 18%. They have average corrosion resistance and poor fabrication characteristics. Heat
treatment methods do not help with hardening the metal either. They generally have better engineering
abilities than austenitic grades. Unlike austenitic grades, they are magnetic. They also have good
resistance to stress corrosion, resulting in lower corrosive material wear.
Ferritic stainless steel are typically used in:
 Vehicle exhausts
 Fuel lines
 Cooking utensils
 Architectural trim
 Domestic appliances

c) Duplex stainless steel
Duplex stainless steel has high chromium and low nickel contents. This gives duplex stainless
steel microstructures that include both austenitic and ferritic phases. They include alloys like
2304 and 2205. These alloys are so named due to their respective compositions - 23% chromium,
4% nickel and 22% chromium, 5% nickel.
Duplex stainless steel typically finds application in areas like:
 Heat exchangers
 Marine applications
 Desalination plants
 Food pickling plants
 Off-shore oil & gas installations
 Chemical & petrochemical plant
d) Martensitic stainless steel
This type of stainless steel consists of high carbon and lower chromium content. Like ferritic grades, it
is magnetic. It does display poor weldability compared to other grades but it has higher hardenability
and can be heat treated to improve properties. Martensitic stainless steel will have lower corrosion
resistance when compared with austenitic and ferritic grades with the same chromium and alloy
content.
 Knife blades
 Cutlery
 Surgical instruments
 Fasteners
 Shafts
 Spring

2.5 Spring steel
Spring steel is a name given to a wide range of steels used in the manufacture of springs,
prominently in automotive and industrial suspension applications. These steels are generally low-
alloy manganese, medium-carbon steel or high-carbon steel with very high yield strength.
Spring steel is known to be resilient and pliable with high yield strength. It has the unique ability
to be formed, shaped, and post heat treated. These physical characteristics are what allow spring
steel to be a general use steel.
i) Composition
Most of the springs are made with medium and high carbon steels, alloy steels and stainless
steels as given below.
Medium and high carbon spring steels – These spring steels are the most commonly used
materials since they are less expensive, These materials can be easily worked and are readily
available. These steels are not suitable for springs operating at high or low temperatures or for
shock or impact loading.
Alloy spring steels – These spring steels are used for conditions of high stress and shock or
impact loadings. These steels can withstand a wider temperature variation than high carbon
spring steels and are used in either the annealed or pre tempered conditions. Silicon is the key
element in most of the alloy spring steels. A typical example of alloy spring steel contains 1.5 %
– 1.8 % silicon, 0.7 % – 1 % manganese, and 0.52 % – 0.6 % carbon.
Stainless spring steels – The use of stainless spring steels has increased in recent times. There
are compositions available which can be used for temperatures upto 300 deg C. All these steels
are corrosion resistant but only the stainless steel of 18-8 composition is to be used at sub-zero
temperatures.
ii) Application
As general use steel, spring steel has a wide range of commercial applications. It is a common
material used for manufacturing objects like springs, washers, saw blades, lock picks, antennas,
and scrapers. It's also commonly used to create lawnmower parts, the landing gear of small
aircrafts, and vehicle coil springs.

2.6 Steels for following materials:
Sl No
Steels for
following
Steel Material Type
1 shaft
The material used for ordinary shafts is carbon steel of grades 40 C 8, 45 C 8,
50 C 4 and 50 C 12. Shafts are generally manufactured by hot rolling and
finished to size by cold drawing or turning and grinding.
2 axles
Axles are typically made from SAE grade 41xx steel or SAE grade 10xx steel.
SAE grade 41xx steel is commonly known as "chrome-molybdenum steel" (or
"chrome-moly") while SAE grade 10xx steel is known as "carbon steel".
3 bolts
Carbon steel is the most common type of steel used in fastener production.
Grades 2, 5, and 8 are typically the standard for carbon-steel based screws and
bolts, with alloyed carbon steel being a higher-end variation on these metals.
Stainless steel is used primarily for long lasting applications, due to its
corrosion-resistant nature and durability. Stainless is a soft metal due to the
low carbon content, therefore most stainless steel bolts are cold-formed and
not heat treated or thru-hardened.
4 nuts
Alloy Steel is the most common material that fasteners are manufactured
in. Alloy steel fasteners are often treated, coated or plated with zinc for
additional corrosion resistance. Alloy steel is used for the hot dipped
galvanized process, treated in a molten zinc bath which creates a tightly
bonded alloy finish.
5
Agriculture
Equipment’s
Low carbon steel is used extensively in the construction of farm machinery.
Frames and most of other members are made out of low-carbon steel. Hot-dip
galvanized steel provides corrosion protection that can often last for decades,
even when exposed to the harsh environment of farming.
Stainless steel is also utilized for its surface properties. With a standard, shiny
finish, it makes it particularly easy to clean. Also, in applications like dairy
farming, the smooth finish is important because of the need to maintain
microbiological quality in the raw milk.
6
household
utensils
Stainless steel finds many applications in the manufacture of kitchen utensils.
7
Antifriction
bearings
Most ball bearings are made of a type of steel known as high
carbon chromium steel, often called chrome steel. This is used for reasons
of cost and durability. Bearings are also made from other materials such
as stainless steel, ceramics and plastic.

2.6 Designation and coding (as per BIS, ASME) of plain & alloy steel and cast iron.
BIS System of Designation of Steels
Some material has names like 40C8, 50C8. Engineering materials have various compositions,
types, Applications, properties. Every material has its different mechanical properties, The
Bureau of Indian Standards (BIS) have standardized the designation method for steel and other
material. These standards are mainly followed by Indian industries, other countries may be using
ASME standard.
i) Designation of Steels
Steels are designated by a group of letters or numbers indicating any one of the following three
properties.
1. Tensile strength;
2. Carbon content; and
3. Composition of alloying elements.
Steel, which are standardized based on their tensile strength without detailed chemical
composition, are specified in two ways- a symbol Fe followed by the minimum tensile strength
in N/mm2. Another method is FeE steel followed by the yield strength in N/mm2.
For examples:
Fe350 – This indicates a steel with a tensile strength of 250 newtons per mm square.
FeE 250- yield strength of 250 N/mm2.
ii) Designation of Plain Carbon Steels:
This consists following three quantities:
1. Figure and indicating 100 times the average percentage of carbon.
2. a letter C
3. a figure indicating 10 times the average percentage of manganese.
Example: 55C4 indicates a plain carbon steel with 0.55% carbon and 0.4 % manganese.

iii) Designation of Alloy steels:
The designation of alloy steels consists of following quantities:
1. figure indicating hundred times the average percentage of carbon
2. Chemical symbol for allowing elements always followed by the figure for its average
percentage content multiplied by the factor. The multiplying factor depends upon the
alloying element and it’s shown in the following figure.
In alloy steels, if manganese % is more than 1 then chemical symbol and their figures are
arranged in descending order of their percentage content.
Example:
25Cr4Mo2 is an alloy steel having an average 0.25% of carbon, 1% chromium, and 0.2 %
molybdenum.
iv) Designation of Cast Steels
Components from cast steel are manufactured by pouring the molten steel into the mold.
There are two varieties of steel castings
1. Carbon steel castings and
2. High tensile steel castings.
Cast steels are designated according to the tensile strength.
Example:
CS640 is a steel casting with a minimum ultimate tensile strength of 640 N/mm2.
Examples of Designated Materials.
(i) FeE 230 (ii) FG 200 (iii) 35C8 (iv) X20Cr18Ni12
i) FeE 230 –steel (Steel having a yield strength of 230 N/mm2) with a minimum tensile strength
of 230 N/mm2
ii) FG 200- Grey cast iron with a minimum tensile strength of 200 N/mm2
iii) 35C8- Means carbon steel containing avg. percentage of carbon is 0.35 and avg. percentage
of manganese is 0.8.
iv) X20Cr18Ni12 –Means alloy steel with an average percentage of carbon is 0.20, the average
percentage of chromium is 25, the average percentage of nickel is 12

Materials for Engineering Unit II

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Materials for Engineering Unit II